There are various methods in gas analysis technology for determining the gas concentrations of the components of gas mixtures.
For example, the method of gas chromatography is widespread. Here, the gas mixture to be tested is injected into a separation column that the carrier gas flows through. The substances of the gas mixture are transported by the carrier gas in the separation column, a rapid and extensive separation of the gas mixture being brought about by means of a constant temperature within the separation column or by means of a controlled temperature increase. At the outlet of the separation column, a detector identifies when one of the substances of the gas mixture leaves the separation column. The electronic signal identified by the detector can be registered as a peak and the composition of the gas mixture can be identified from this signal by means of appropriate evaluation software. The measuring set-up and execution of the procedure in gas chromatography are time consuming and structurally complex.
In addition to gas chromatography, it is generally known to use the differences in the thermal conductivity of the gases concerned in order to determine concentrations of individual gases of a gas mixture.
In principle, a resistance heating element acting as a heat source is brought up to a temperature that is higher than that of its surroundings by means of current flow. Heat from the gas to be tested is conducted via a heat conduction path defined by geometric parameters from the resistance heating element acting as a heat source to a heatsink that is kept at a constant temperature. As a result of the heat transfer from the resistance heating element to the heatsink, energy is drawn from the heat source, said energy representing a measure for the heat conductivity of the gas which can be measured using appropriate methods.
The method for identifying gas concentrations of gas mixtures by means of the heat conductivity of these gases is carried out for the various gas components using different temperatures of the resistance heating element.
In order to measure the gas concentration, on the one hand a plurality of heat conductivity sensors corresponding to the number of gas components can be used. Alternatively, the use of one heat conductivity sensor is conceivable in which the resistance heating element is heated up to different temperatures at certain intervals depending on time.